It only works with Facetime group call, which has been disabled: https://techcrunch.com/2019/01/28/apple-disables-group-calling-in-facetime/
⚠️🚧iPhone user beware Major FaceTime bugs🐛🐜
Take care what you say on your phone. On ANY phone, not only the I phone . Because this effect is normal GSM standard…from GSM point of view: no bug, but a feature …
What I mean: first think, then speak. Do not say “now I have to call this stupid b…”
Even better: do not think it.
Either call him …
or not.
I remember my old sprint phone would do this when people called me. I could hear them clearly before choosing to answer or decline.
But the other way around? Yikes!
I remember there was a way to trick old GSM phone of the pre-smartphone era to answer a call without ringing and without the owner pressing any buttons. You could sneak-listen as long as the person didn’t use the phone and had battery - which lasted days then.
Also, before digital cellphones, with the right amateur radio equipment you could listen to random calls without any of the callers noticing. My dad was a hobbyist radioamateur when cellphones started showing in Brazil. There weren’t many cellphones that time, so you had to be patient to find the frequency, but it was rather easy.
Well, doubt anyone saw this one coming